by Barry Talyor
What amazing mineral Quartz is, with its beautiful often perfectly formed crystals, it certainly has an aura of mystique about it. In fact magical would not be far from the truth as Quartz has always been believed to have special powers. In ancient European history people believed that quartz was actually ice from the mountains, frozen solid over millennia and as such it could never thaw.
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Later, the Romans believed that if you drank wine from a goblet made of a variety of quartz called Amethyst you would never be drunk, the word Amethyst in ancient Greek in fact means not intoxicated. When we look beyond the spellbinding beauty of its crystals to the folklore that surrounds it, this mineral holds a very special place in our hearts and minds compared to many other minerals. Quartz is formed from building blocks of one Silicon atom combined with two Oxygen atoms, Si O2. Building blocks of this basic composition share oxygen atoms that fit together in a regular pattern (Si 04), often in classic six sided crystals. There are two distinct structural varieties of quartz crystals, a low temperature and a high temperature form; both depend upon the atmospheric pressure as well as the temperature in the environment that they form in. Crystals grow and develop from initial silica rich fluid, this fluid is affected by the silica saturation level, any impurities and the temperature for the seeding process to start. The fluids from which the crystals form are considered to exist as a silica rich colloid (see article in Rock n gem issue 35 spring 2006), the components then rapidly coalless and crystallise.
Uses for Quartz One amazing feature of quartz is the strange piezoelectric property, for example this means that if a small sample is squeezed in one direction, it will emit an electrical charge and this property is used in gas flame ignition. It is really a truly remarkable mineral, also when a sample of quartz is subjected to a small electrical charge from a battery, it will vibrate at a high level; this constant vibration level is then used to regulate each second of time in Quartz watches, hence the name. Initially the necessary quartz was mined for this purpose but it was later discovered that in nature quartz exists in a combination of two slightly different atomic configurations, left and right handed crystals. When grown commercially, man made quartz can be produced in either just right or left handed form, this provides the best constant vibration level for accuracy in timekeeping. Looking at the other powers of quartz, another of its unique properties is used in televisions, radios, computers and mobile phones as a transmitter and receiver. Some of you may remember the old crystal radio sets from childhood and these used quartz to receive the radio signals. Finally we should not forget that quartz is also used as an abrasive in sandpaper and as a key component in the manufacture of everyday glass. More controversially it is used in the practice of crystal healing, here its magical qualities called the metaphysical properties are used by new age health and wellbeing practitioners.
Alpha low temperature quartz The usual temperature at which the more common (Trigonal) quartz crystals grow is in the range of between 180 and 573 degrees centigrade. This is known as the low temperature form of Quartz, the temperature of crystallisation has been determined by heating quartz with inclusions and observing any changes in the inclusion (from the Crystal phase to Gas/fluid phase and back).
Alpha Quartz point from Minas Gerais, Brazil
Angel Aura or Opaline Quartz, USA (infused with Platinum/Silver)
Low temperature quartz can be further subdivided into three distinct types; this is based on the appearances of crystals. These three quartz crystal forms are the lamellar, the Alpha low temperature and the Alpine low temperature. Lamellar crystals are flattened hexagonal crystals with a cross section of 4 short sides and 2 long sides. Asimilar type of flattened quartz crystal called Faden Quartz will be looked at in part 2.
Alpha low temperature quartz crystals are six sided columns usually with a single point or natural termination; this type often exhibits both phantoms and inclusions. The primary Alpha low temperature quartz can easily be recognized by the external hexagonal structure of the crystals prisms, together with the hardness of 7 on the mohs scale. Phantoms are common in Alpha Quartz, these are usually seen as ghost stepped internal layers of multiple growths these are parallel to the column sides. In a different phantom structure, a rarer more solid quartz crystal or even multiple individual crystals can be observed fully formed inside another crystal. This type of inclusion is found growing in from the sides and not from the base of the columns, growing inwardly but at a different angle to the host crystal.
Alpine low temperature Quartz crystals sometimes grow parallel to the host rock cavity wall as opposed to perpendicular, these are as doubly terminated crystals and this form of growth was initially observed in amazing crystals from the Alps which were attached to the host rock by one side.
Beta Quartz The quartz formed at high temperatures produces crystals in the Hexagonal as opposed to the Trigonal crystal structure of Alpha quartz, Beta quartz is produced at temperatures of over 573 degrees centigrade, crystal form as doubly terminated versions with a diamond shape, this type is mainly found in Rhyolite. Beta quartz is unstable and unless cooled very quickly will subsequently change to Alpha quartz, this is a pseudomorph after the Beta Quartz and is referred to as Chiral Structure. The Alpha quartz after Beta quartz is usually found as a double pyramid but now converting to the more stable Alpha Quartz with additional faces, retaining the basic Beta Quartz diamond shaped external structure. Care should be taken as a close comparison to the double terminations exist and can have the additional initial Alpha quartz faces.
Colour Variations The common low temperature alpha crystalline quartz material is the more stable growth form and therefore the one most often found. With more detailed knowledge the Left and Right handed forms can be identified. Alpha quartz usually exists as pyramidal columns, they also display the usual common colour variations, these exist due to minor microscopic inclusions of common elements, in effect these are atoms as contaminants of the original silica fluid. Exceptions to this pattern are dislocations in the structure giving the Black and Smoky types of Quartz, these varieties form by irradiation both natural and artificial, the natural decay of radioactive elements affect the quartz crystals whilst in the host rock. Recently many other colour variations have been added artificially to existing quartz crystals, this is by applying a microscopic coating of minerals such as Gold, Silver and Cobalt. Afine coating of microscopic gold produces Aqua Aura blue crystals for example. Variations in both the colour and crystal form are seen in most mineral books and also at the many mineral dealers’ shows.
Clear quartz Clear or even water clear crystals called Rock Crystal can be found, many of these will have been polished for sale at gem shows. These crystals can display beautiful inclusions and also well formed phantoms and refractive rainbow layers derived from internal fractures. The inclusions most commonly seen in the Alpha Quartz are fine needles either of Rutile, Tourmaline, Amphibolite or Lepidocrosite; articles about all these inclusions can be found in several back issues of Rock n gem.
Phantom quartz Crystals of quartz often grow in a rhythmic pattern as the variables of temperature and the silica saturation levels constantly change as long as the silica rich solution that surrounds the crystals remains. Changes in the rate of crystallisation occur as the silica saturation levels in the fluid fluctuate thus modifying the growth rate; this can be seen in the many layered phantoms within crystals. Sometimes floating crystals and broken fragments can also be seen inside clear quartz crystals, this is due to tectonic movement in the host rock during formation. It should be noted that many beautiful phantom crystals for sale have been polished and can be easily identified by the smooth crystal sides and also often the bevelled bases that are applied for aesthetic reasons.
Smoky quartz Often crystals are found in a natural brownish or grey colour as well as black crystals, some have been treated with irradiation from x ray machines, these crystals are mostly jet black and this colour type is called Morion, supposedly named after the Irish Mourn Mountains where they were first described. Dark speckled crystals coloured by inclusions of Haematite produce a similar colour but can be seen to be sparkly with fine speckles of haematite; this type is most frequently found in material from the haematite mines of Cumbria in the southern Lake District, often these have beta quartz type structure.
Amethyst quartz Light or dark purple varieties of this quartz are caused by un-oxidised widely dispersed atoms of iron. Poor quality amethyst quartz is often heat treated to oxidise the iron content and produce what is called burnt Citrine, a brownish yellow variety. Amethyst Flowers form not in the usual parallel growth points but with crystals that are flattened in the horizontal plain. These crystal growths are carefully removed from the heavily altered host rock, part of which often remains attached. These are found in Brazil between Irai and Planalto in the Rio Grande do Sul province.
Inclusions Quartz Inclusions in crystals have been by some reports confusingly been divided into a primary type found in low temperature quartz and a secondary type in higher temperature quartz. The higher temperature inclusions are Haematite and Anthraxolite with lower temperature being Rutile, Actinolite and Tourmaline. As mentioned before inclusions can be composed of Rutile, Tourmaline, Actinolite or Lepidocrosite. Other inclusions can be of Pyrite, Marcasite, Fluorite, Amiant (Amphibole) and Lodolite (non specific inclusions) as well as the Feldspars and Micas. Crystals with inclusions are commonly found in alpha quartz, there is a huge variety of other minerals that can be trapped within the growing quartz. Garden quartz, Landscape quartz and Lodolite quartz are all in fact common terms frequently used for various minor inclusions of the host rock. Other types of inclusion are referred to more specifically when they can be readily identified such as Calcite or Mica, the thin rods or needles of many colours and forms will be treated separately in part 2.
Growth of Quartz inclusions Of all the types of inclusions found, the most common of the visually striking needle like forms are Titanium minerals known as Rutile. I have seen it argued that the needles grew first but it is clear to me that in many cases growth must often be contemporaneous, Chalcedony as found in Agates is a separate form of silica rich mineral and this seems to have the ability to incorporate pre-existing minerals, usually Zeolite in Vein Agates for example.
for other articles in the quartz and chalcedony series:
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